New nucleoside and nucleotide analogues will be prepared and studied as antiviral antitumor agents.These compounds will include (i) gem-bis-(hydroxymethyl)methylenecyclopropanes, (ii) cyclicphosphates of gem-bis-(hydroxymethyl) methylenecyclopropanes, (iii) lipophilic phosphoralaninate prodrugs of gem-bis-(hydroxymethyl)methylenecyclopropanes, (iv) 7-(2-amino)purine analogues, (v) phosphonateanalogues of methylenecyclopropanes and (vi) resolution of R and S diastereoisomers of phosphoralaninate methylenecyclopropane prodrugs,synthesis of the respective phosphorothioates and study of stereochemistry of intracellular activation.